Analytical apparatus and process

ABSTRACT

A low load analytic system is proposed, comprising a cuvette divided into separate chambers by a porous barrier which may be free to move inside the cuvette, and a test reagent in one compartment. The barrier may be floating on the reagent. The barrier may be microporous or be a semipermeable membrane, hydrophobic or hydrophilic, depending on the test. In one mode, the cuvette is the barrel of a hypodermic syringe and the test reagent is held in the far compartment, in the barrel of the syringe. Numerous modifications of the system are also disclosed.

O United States Patent 1191 Padawer 1 1 Feb. 11, 1975 [54] ANALYTICAL APPARATUS AND PROCESS 3,480,399 11/1969 Hamilton 23/253 R P 3,539,300 ll/l970 Stone 23/253 R [751 lnvemol- JacqPes Maw", 3,573,470 4/1971 Haley 356/246 ux flastmss-on-Hudson. NY 3,657,073 4/1972 Burton et al.... 195/127 [73] Assigneez Ame" Einstein College of Medicine 3,660,037 5/1972 Sokol 2 3/253 R of Yeshiva University Bronx NY. 3,706,381 l2/l972 Joynes et a]. 23/253 R X 3,748,098 7/l973 Dutch 23/253 R [221 Filed OTHER PUBLlCATlONS [21] Appl- 338,358 Searcy, Diagnostic Biochemistry," p. 274 (1969).

Related U.S. Application Data [63] Continuation-impart of Ser. No. 262,183, June l3, Pr'mary Examlner"j9seph Scovronek 1972, abandoned. Attorney, Agent, or Fzrm-B1erman & Blerman [52] U.S. Cl. 23/230 R, 23/230 B, 23/253 R, [57] ABSTRACT 23/254 195/103 195/5 195/127 356/246 A low load analytic system is proposed, comprising a [51] Int. CL... G0ln l/l0,G0ln 31/00, G0ln 33/16 H d t t h b b 58 Field of Search 23/230 R 230 B 253 R e e y a 23/259 292 206/47 219 356/246f barrier wh1ch may be free to move 1ns1de the cuvette, 95/127 128/2 and a test reagent in one compartment. The barrier may be floating on the reagent. The barrier may be microporous or be a semipermeable membrane, hy- [56] References cued drophobic or hydrophilic, depending on the test. In UNITED STATES PATENTS one mode, the cuvette is the barrel of a hypodermic 2,888,331 5/1959 Carpenter 23/253 R syringe and the test reagent is held in the far compart- 3,000,706 9/]96l Royce 23/254 R X ment in the barrel of the syringe Numergus modifieag tions of the system are also disclosed. 0e ere a. 3,367,850 2/1968 Johnson 23/254 R X 17 Claims, 13 Drawing Figures PHEHTEB FEB! 1 I975 SHEET 1 BF 2 PATENTED FEB] H975 SHEET 2 OF 2 ANALYTICAL APPARATUS AND PROCESS This application is a continuation-in-part of copending application Ser. No. 262,l83 filed June I3. 1972, now abandoned.

This invention relates to apparatus for performing chemical analysis and in particular to small load operation biomedicaltest needs.

Recent advances in biochemistry have engendered many biomedical diagnostic tests useful to the practicing physician. Tremendous numbers of biomedical tests are routinely carried out daily in hospitals and in independent medical laboratories, some even in the doctors office. The very number of tests has created a demand for automated test procedures and equipment, and a well-equipped medical laboratory can routinely conduct tests by the thousands. However, creation of automated test facilities does not constitute a complete response to the ever-increasing usage of test procedures. Instances will always arise wherein the automated facilities of the biomedical laboratory are simply not available, for example, off-hour emergencies and isolated geographical areas.

Accordingly, a real and substantial need exists for small load analytic systems capable of operation by relatively untrained technicians. The object of this invention is to provide improved small load analysis systems.

Basically the rationale of the present invention is that many of the chemical reactions involved in biochemical tests can be carried out in a multichambered cuvette. The desired components of the sample can transport across a porous membrane from a sample chamber into a second chamber of the cuvette, to there undergo a chemical reaction indicative of that reactant. Thus, for example, the available CO present in a sample of blood or another fluid will diffuse from a sample chamber through a hydrophobic semipermeable membrane (e.g., Teflon) into a chamber containing an aqueous alkaline solution of a color reagent like phenolphthalein and react therein with the solution, changing its color. A colorimeter measurement taken of the color indicatorsolution will serve to determine accurately the available CO present in the sample. If the sample chamber contains an acid reagent in addition, then the total CO content of the original sample will be released to diffuse through the membrane and the colorimeter reading will measure the total CO in the sample.

For further understanding of the invention, reference is now made to the attached drawings wherein:

FIG. 1 diagrammatically illustrates the basic structure of the multi-ch'amber cuvette;

FIG. 2 is an exploded perspective of one form of the barriers of the invention;

FIG. 3 illustrates a modified form of multichambered cuvette;

FIG. 4 is a diagrammatic view of another embodiment of the invention;

FIG. 5 is a modification of the device of FIG. 4;

FIG. 6 is a diagram of another embodiment of the invention with membranes at right angles to each other;

FIG. 7 is a diagram of an embodiment of the invention using electric potential to assist in carrying out the test;

FIG. 8 shows a diagrammatic cross-section of a modification of the cuvette or barrel which eliminates or reduces distortion caused by curved sides;

FIG. 8A is another way to eliminate or reduce curvature distortion by the use of lenses;

FIG. 9 is a convenient way of maintaining the membranes at the desired distance from each other;

FIG. 9A is a modification of the device of FIG. 9 wherein the membranes are separated by a tube;

FIG. 10 is a diagram of the device of FIG. 9A mounted in a sled ready for insertion into the cuvette or barrel; and

FIG. I] is a diagram ofa form of the invention capable of carrying out two tests on the same sample at the same time.

Referring now to the drawings, it may be seen that the basic structure of the present invention involves a vial or cuvette l0 separated into at least two (three being illustrated) chambers or compartments l2, l4 l6 fixed in place by barrier spacers l8 and 20. In the basic form of the invention shown in FIG. 1, cuvette I0 is sealed at its open end by a cap 22. Chambers 14 and 16 are filled by appropriate test fluids. Although in the form illustrated in FIG. 1 chamber 12 is empty of test reagent, inclusion of a test reagent in chamber 12 is also contemplated. For purposes of the analysis, chamber 12 is charged with test sample, e.g., by aperturing cap 22 with a hypodermic needle and forcing the sample in through the needle.

An important aspect of the present invention is that all the analytic tests contemplated for the present cuvette structure involve passage of one component derived from the test sample through a porous barrier. Normally the barrier is a semipermeable membrane, but for some tests the pore size of the barrier may be larger. Accordingly, the carrier can best be described as porous, including within the meaning of the term, microporous membranes and semi-porous membranes. The barrier may be hydrophilic or hydrophobic in na ture. The exact character of the membrane is predetermined by the analytic test for which the cuvette is constructed. However, all of the analytic tests for which the present cuvette structure is adapted require that the barrier prevent migration of all interfering component or components. To repeat, the tests involve transport of some desired component or constituent from the test sample across the barrier 18 into the test fluid in chamber 14. In those tests where the analytic procedure requires a second reaction, an additional barrier 20 and chamber 16 are provided. In such instances, the reaction in chamber 14 creates or liberates a component which transports from the fluid in chamber 14 through the barrier 20 into chamber 16.

The cuvette structure of the present invention normally is employed with an optical read-out instrument which, depending on the analytic test, may be a colorimeter, a fluorometer, a nephelometer, in short. any of the many optical systems already being employed to measure chemical, biochemical or biomedical test results. Therefore, cuvette 10 is sized to fit into whatever standard optical measurement device is appropriate to the particular test for which the cuvette has been constructed. Appropriate optical measuring equipment is widely available commercially, and virtually every analytical test where optical measurement of the test results is made has been calibrated to standard optical equipment, e.g., colorimeter, nephelometer, fluorometer, etc. Actually, many of the recent advances in auto mated analysis have involved a change in analysis technique or chemistry so that the test results can be meaured by optical means.

A principal object of the present invention is to provide a manual one-at-a-time or low-load counterpart to widely used automated analysis systems. Practice of this invention contemplates making the test results (automated or manual) strictly comparable. Repeat tests or later tests analyzed in the automated laboratory can be compared directly to the results of the manual test carried out in the cuvette structure of the present invention.

Since many of the analytical test procedures to which the apparatus of the present invention is adapted require liquid phase to liquid phase transport of one component through a porous membrane, the porous barrier layer structures and filling procedures should minimize creationof air bubbles so that the barrier maintains liquid on both surfaces thereof. To insure such complete contact, practice of the present invention according to one preferred mode thereof involves floating the barrier. The barriers 18, 20 may be made free to move inside cuvette 10. Their exact position within cuvette 10 is determined entirely by the volume of fluid in the chambers 14 and 16 bound bybarriers 18, 20. Thus, barrier 20 floats, so to speak, on the test fluid inside chamber 16; barrier 18 floats on the test fluid inside chamber 14. Needles to say, the dimensions of cuvette 10 must be uniform and accurate, so that free barriers l8 and 20 can slide the length of cuvette 10 and still seal against fluid leakage from chamber to chamber.

In some cases, a small air bubble may deliberately be introduced into chambers containing the liquid reagents so as to act as a means of mechanical mixing; e.g., by rotating or vibrating the device. Mixing would favor reaction rates and reduce back diffusion of reaction products, thus shortening the time required for the test. In other cases, reaction rates are so fast that no mixing is necessary.

Illustrated in FIG. 2 is a preferred form of barrier, wherein porous membrane 30, which may be a microporous membrane or a semipermeable membrane which is hydrophilic or hydrophobic, depending on the analysis involved, is a circular piece sandwiched peripherally between centrally apertured members, hoop 32 and 34. These three members are fused, glued or otherwise secured to form a unitary barrier structure. The hoop portions 32, 34 of the barrier constitute a continuous foot having significant bearing area contacting the inside wall of cuvette'10. This ensures that the barrier has sufficient structural rigidity to prevent buckling and makes certain that the porous barriers l8 and 20 remain across cuvette l and freely rest on the underlying test liquid. For assembly purposes, circular membrane 30 and hoops 32, 34 are preferably made of thermoplastic materials. They may. be heat joined readily; the hoops may be directly molded on around the peripheral edge of porous membrane 30 which may be bonded chemically to one of the hoops. For filling the cuvette mode illustrated in the drawings, an air vent or aperture (not shown) may be provided through hoops 32, 34.

A satisfactory way of providing the device depicted in FIG. I is to start with a cuvette having a venting hole at the bottom. Barrier 20 is then introduced, and advane ed a set distance down the. tube, the reagent for chamber 14 being layered over it so that when the proper amount is reached, its meniscus forms a convex surface atthe lip of the tube. Barrier 18 is then deposited on this 'l iquid surface and pushed some distance down the tube, pushing barrier 20 and reagent l4 further down in the process. The device is then inverted, the proper reagent for chamber 16 is delivered atop barrier 20 through the vent hole, barrier 18 is pushed up to expel residual air in chamber 16, and the vent hole is then sealed.

A modified form of cuvette is illustrated in' FIG. 3. The cuvette is part of a hypodermic syringe arrangement, being the barrel of a standard hypodermic syringe with the usual plunger 102 structure closely fitted thereto. A restraining yoke 104 on the rear of barrel 100 serves to limit rearward movement of plunger 102 and assures that a predetermined volume of sample fluid is taken up through the needle 106. A protective cap 108 may be used to surround and shield needle I06 and keep it bacteriologically sterile, if desired.

A procedure, similar to that relating to the device of FIG. 1, can be followed for filling the modified form of the device shown in FIG. 3, except that the needle acts as a venting hole to allow filling the reagents and barriers from above, and that barrier 112 is then advanced until fully seated near the needle, thus reducing the prospective sample chamber volume to nearly zero.

In the construction illustrated by FIG 3, two spacedapart floating porous barriers 110, 112 are provided. For many, and perhaps most, biomedical tests only one such barrier is required. In the illustrated mode, one test reagent is in barrel chamber 114 between barriers and 112, and a second test reagent is in barrel chamber 116 between plunger 102 and barrier 110. The volume 118 between 112 and the needle 106 may be air filled, evacuated, or filled with a dliuent such as saline solution.

For conducting a test, the protective cap 108 is removed, and a predetermined quantity of sample, e.g., expired air or blood, is drawn through needle 106 into sample region 118 by rearward movement of plunger 102 to the limited end of its rearward travel. As plunger 102 is drawn back, the porous barriers 110 and 112 and the test reagents in chambers 114and 116 are drawn rearwardly (by the suction), enlarging chamber 118 as the sample is drawn into it. Thereafter, a component from the sample or test reagent traverses porous barrier 112; for example, in a total CO test, I-I+ ion crosses barrier 112 from the sample chamber, then CO diffuses across barrier 112 entering chamber 114, crosses chamber 114, traverses porous barrier 110 and enters the test reagent inside chamber 116 altering an optical characteristic of the reagent. After a given time interval, the cuvette is inserted into an optical instrument, the optical path being, for example, along line X- X through barrel 100 which normally is transparent glass or plastic, and through the test solution in chamber In a particular embodiment of the invention, the reaction takes place on or within the membrane itself. Normally, such amembrane would be transparent or at least translucent in order to make the test results It is also within the scope of this invention to use a syringe having a hollow plunger. The hollow in the plunger can then act as a chamber to hold a reagent, in which case the leading face of the plunger consists of an appropriate barrier, or it can contain a standard solution to be used as a comparison for the color change resulting from the test reaction, in which case the end is sealed. In FIG. 4, hollow plunger 36 fits inside syringe barrel 11 with membrane across its mouth. Sample chamber 37 is provided and the reaction takes place in substantially the same way as in the device of FIG. 3, except that the hollow plunger 36 forms one of the chambers.

In FIG. 5, sample chamber 37 and reagent chamber 38 are separated by barrier 35. Standard chamber 39 is provided in hollow plunger 36 to hold a reference solution to assist in comparing the results of the test with a desired standard.

FIG. 6 shows a device having a hollow plunger 36 carrying membrane 44 with its plane axially aligned. Another membrane 43 is placed as in the device of FIG. 5. A light source 51 and a photoelectric cell 52 are so positioned as to permit a beam of light to pass through membrane 44 and impinge on cell 52. Any change in opacity of membrane 44 can easily be read.

This form of the device is particularly suitable for use with samples which are not clear, such as blood. Membrane 43 prevents the passage of the occluding components of the sample (e.g., blood cells) so that reagent chamber 38 contains only clear material which will not interfere with the effect of the test reaction on the light beam and photoelectric cell 52.

This embodiment is also useful inn those situations in which a reaction product is precipitated on or within the barrier, that is, in which the desired sample component passes through barrier 43, diffuses freely through a carrier fluid or reagent in chamber 38, and then reacts on the surface of a within the body of barrier 44 to produce a color deposit or a change in the membrane lucency. In some cases, indicator particles may adsorb on the barrier surface.

The plunger 36 ofthis embodiment can, of course, be

used. in accordance with the devices of FIGS. 3, 4 and 5 as well as in the manner heretofore described.

4 In yet modification of this invention as shown in FIG. 7, an electromotive force is impressed across syringe l0 and plunger 41 by means of conductor connected to a source of current 42. This can be alternating or direct current, or a variant thereof, to help drive the reagent and/or sample in the desired direction.

In certain types of visual or photometric measurement, the distortion caused by curvature of the cuvette or barrel is undesirable. This can be minimized or eliminated by the devices shown in FIGS. 8 and 8A. In FIG. 8, a barrel 11 is shown which has four flat portions 49. Light source 51 is directed through portions 49 to give an undistorted view of the results of the test. This is particularly useful in nephelometry, since the Tyndall effect can be observed readily by viewing at a right angle to the light beam. Of course it is not necessary to have flats all around, since it is not always necessary to view in all directions. Only those portions through which it is intended to view need be flat.

This same problem can be solved by the device of FIG. 8A. Here, in order to minimize the distortion (or lens effect) caused by the curved cuvette or barrel,

compensating lenses 50 are formed in or attached to the cuvette or barrel 1] in the viewing area.

In those forms of the invention in which a double membrane is desirable, the embodiment of FIG. 9 will prove useful. Membranes 43 and 44 are held in the desired relationship to each other by spacer rods 45. This has the advantage of fixing the distance between the barriers and preventing them from jamming or leaking.

A variation of this form is shown in FIG. 9A. Instead of a plurality of spacer rods, hollow tube 47 extends from barrier 43 to barrier 44.

In FIG. 10, there is shown a device using the tube structure of FIG. 9A. Sled 46 surrounds tube 47 and is intended to fit within the barrel of cuvette. Portions 53 seal against the inner wall of the cuvette or barrel substantially preventing passage of fluid except selectively through barriers 43 and 44 of tube 47.

A still further modification of the invention is shown in FIG. 11. Barriers 43 and 44 may be the same or different. Similarly, reagent chambers 38 and 38a may contain the same or different reagents. Sample chamber 37 is common to both reagent chambers. This form of the invention permits the running of two tests simultaneously in the same apparatus using a single sample. It can also be used to incorporate a standard for comparison to the test result. In the latter case, no barrier is present on one side of the plunger and the standard is sealed in.

As can be seen from the foregoing description, the present invention is useful for conducting one test at a time. The structure has the advantages of being lightweight, portable, self-contained, and is well suited for use directly in a physicians office, at bedside, even in an ambulance or in other emergency situations. The test device can be employed in hospitals during off hours, when the automated laboratory equipment is down and laboratory personnel are unavailable. Few special skills are needed to conduct the tests and unskilled nursing or paramedical personnel, regulatory agency personnel (for food inspection, environmental control, police, etc.) can conduct the analyses accurately. In some instances, the ultimate reaction product is stable enough so that the test may be stored, e.g., for legal purposes.

Although the test procedures and reagents form no part of the present invention, the widespread applicability of the multi-chamber cuvette described above is noteworthy. The following tests can be carried out therewith:

BUN Uric Acid Alcohol (blood/ Bilirubin Glucose expired air) Albumin Carbon Dioxide Transaminase Ammonia Carbon Monoxide Alk. phosphatase Antigen-antibody reactions Many of the analytic tests, such as for example, the available CO test, require only a single barrier cuvette.

Other tests require the two barrier assemblies as illustrated in the drawing. One such test is the determination 0 uric acid. For this test, the first barrier should be hydrophilic, and may, for example, be a cellophane dialysis membrane. After the blood sample has been drawn into the sample chamber, uric acid present in the blood will diffuse through the cellophane dialysis mem brane into the first reaction chamber, and there react with uricase (present in the preloaded reagent) to produce C0 The CO will diffuse back through the cello phane membrane into the sample compartment, as well as forward into the second reaction chamber. The second barrier should be a hydrophobic semipermeable membrane, being for example, a fluorocarbon dialysis membrane (Teflon). The second chamber test solution is an aqueous alkaline indicator so that the CO crossing the hydrophobic semipermeable barrier will react to cause a color change in the indicator solution. Since the CO product is related to the original concentration of uric acid in the blood sample, an optical color reading of the indicator solution will constitute a measurement of the uric acid concentration in the blood sample.

Another particularly useful test uses hemoglobin as the test reagent. This can be either in liquid form (e.g., as a solution) or in solid form (e.g., microcrystals). This material is particularly useful in testing for carbon monoxide in the presence of various air pollutants such as carbon dioxide, sulfur dioxide, and nitrogen oxides. The following description will be specifically directed to testing for the presence of carbon monoxide, but the principles are,'of course, applicable to other similarly reacting materials as well.

Hemoglobin reacts with oxygen to form-a compound which is a brownish color. Carbon monoxide also reacts with hemoglobin to form a slightly different material which has a cherry red color. Obviously, the color change can be observed visually or colorimetrically and compared with a reference standard if desired.

As an additional variation, a color filter can be placed between a source of radiation (e.g., light) and the test solution. The wavelengths which the filter will pass should be those which correspond with the absorption peaks of the carbon monoxide hemoglobin derivative. These are to be found at 535.and 570.9 millimicrons. Alternatively, a source of mono-chromatic light can be used, again corresponding with these absorption peaks. A radiation-sensitive cell such as a photocell is placed in the path of the beam from the source so that thelight impinges on it after passing through the test chamber. Thus, the changes brought on by the test will result in variations in the amount and type of transmitted light. The photocell can easily and automatically read these. Thismethod will enhance the sensitivity of the test and permit more accurate readings.

A still further improvement on this method and device consists of splitting the radiation into two beams and passing each beam through a separate filter before the beams pass through the reaction chamber. One filter is of the same character described in the preceding to pass, that is, wavelengths such that both the oxygen derivative and the carbon monoxide derivative of hemoglobin absorb equally. There is provided a radiationsensitive cell (in this case a photocell) for each of the beams, and the difference between the two readings is compared. By using this method, the device will automatically correct for variations in source intensity or with changes in airborne particles which might reduce transmission independently of the test reaction (c.g., smoke, fog, etc.).

Of course, these methods can be connected up to an alarm or other warning device which will trip when the concentration of the undesired pollutant reaches a predetermined level. Similarly, a relay could be used to close or open doors or windows or to turn on ventillating fans and the like.

Many of the pollutants found in air are deleterious because they have undesired'reactions with hemoglobin. Some of these reactions'are irreversible and result in permanet damage while others like the carbon monoxide specifically referred to can be reversed if caught in time. For this reason, the use of hemoglobin as a test reagent for various types of pollutants in air is generally suitable. in fact, analogs of the theme moiety of hemoglobins such as polypyridine derivatives are also satisfactory for this purpose.

While only a limited number of embodiments of the inventin have been specifically disclosed, such variations as would be apparent to one having reasonable skill in the art can be made without departing from the scope or spirit thereof. The invention is to be broadly construed and not tobe limited except by the character of the claims appended hereto.

It is obvious to anyone having ordinary skill that these methods can be used with gases as well as with liquids where the nature of the test so permits.

1 claim:

1. An apparatus adapted for chemical analysis com prising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact therewith, a second porous barrier and a second test reagent fluid being present, the second test reagent being disposed in a second compartment on the side of said second barrier away from said first reagent compartment, the second barrier being in direct test reagents.

2. The apparatus of claim 1 wherein said porous barriers are maintained in an axially spaced-apart relationship by at least one spacer extending from said first barrier to said second barrier.

3. The apparatus of claim 2 wher eiii prises a hollow tube.

4. The apparatus of claim 3 wherein there is provided a generally cylindrical sled surrounding at least part of said tube, said sled having at least one sealing portion disposed circumferentially around said sled and adapted to substantially seal against the inner wall of said cuvette. i

5. An apparatus adapted for chemical analysis comrising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a tac with the two sai spacer co first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact there'- with, said cuvette having at least one lens located in an area through which test results are sensed, said cuvette having a curvature in said area, said lens compensating for distortion caused by said curvature.

6. The apparatus of claim 5 wherein there are two said lenses and a source of light directed through both of said lenses.

7. The apparatus of claim 6 wherein said two lenses are on opposite sides of said cuvette, and have their axes substantially in alignment, and a third lens having its axis at substantially a right angle to the other axes.

8. A method of carrying out chemical testing comprising introducing a fluid sample to be tested into a chamber, said sample being in contact with a first porous barrier and a second porous barrier, permitting at said first barrier and contact a first fluid reagent, at least some of said constituents passing through said second barrier to contact a second fluid reagent whereby the light transmission characteristics of at least one of said reagents are altered.

9. The method according to claim 8 wherein said first reagent and said second reagent are the same.

10. The method according to claim 8 wherein said first reagent and said second reagent are different.

11. An apparatus adapted for chemical analysis comprising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact therewith, said apparatus having means to provide an electromotive force across said cuvette in the axial direction towards said barrier, whereby said first reagent is driven across said first barrier.

12. An apparatus adapted for chemical analysis comprising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact there with, said cuvette comprising the barrel of a hypodermic syringe having a needle point extending from one, the test reagent being in the far compartment relative to the needle point, the first reagent compartment being in the plunger of said syringe.

13. The apparatus of claim 12 wherein there is provided a second reagent compartment containing a second reagent, a second porous barrier in contact with said second reagent compartment and said reagent therein, a sample chamber in said syringe adjacent said point, both said first barrier and said second barrier in contact with said sample chamber and the sample contained therein.

14. The apparatus of claim 13 wherein said reagents are different, whereby two different tests can be run simultaneously on said sample.

15. The apparatus of claim 12 wherein there is provided a second compartment in said plunger, said second compartment containing a reference fluid.

16. The apparatus of claim 12 wherein said plunger is of reduced cross-section adjacent the end of said plunger nearest said point, said barrier being on the reduced cross-section of said plunger, the plane of said barrier being parallel to the axis of said plunger.

17. An apparatus adapted for chemical analysis com prising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact therewith, said cuvette comprising the barrel of a hypodermic syringe having a needle point extending from one end, the test reagent being in the far compartment relative to the needle point, there being a chamber in the plunger of said syringe, said chamber containing a ref 

1. An apparatus adapted for chemical analysis comprising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact therewith, a second porous barrier and a second test reagent fluid being present, the second test reagent being disposed in a second compartment on the side of said second barrier away from said first reagent compartment, the second barrier being in direct contact with the two test reagents.
 2. The apparatus of claim 1 wherein said porous barriers are maintained in an axially spaced-apart relationship by at least one spacer extending from said first barrier to said second barrier.
 3. The apparatus of claim 2 wherein said spacer comprises a hollow tube.
 4. The apparatus of claim 3 wherein there is provided a generally cylindrical sled surrounding at least part of said tube, said sled having at least one sealing portion disposed circumferentially around said sled and adapted to substantially seal against the inner wall of said cuvette.
 5. An apparatus adapted for chemical analysis comrising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact therewith, said cuvette having at least one lens located in an area through which test results are sensed, said cuvette having a curvature in said area, said lens compensating for distortion caused by said curvature.
 6. The apparatus of claim 5 wherein there are two said lenses and a source of light directed through both of said lenses.
 7. The apparatus of claim 6 wherein said two lenses are on opposite sides of said cuvette, and have their axes substantially in alignment, and a third lens having its axis at substantially a right angle to the other axes.
 8. A METHOD OF CARRYING OUT CHEMICAL TESTING COMPRISING INTRODUCING A FLUID SAMPLE TO BE TESTED INTO A CHAMBER, SAID SAMPLE BEING IN CONTACT WITH A FIRST POROUS BARRIER AND A SECOND POROUS BARRIER, PERMITTING AT LEAST SOME CONSTITUENTS OF SAID SAMPLE TO PASS THROUGH SAID FIRST BARRIER AND CONTACT A FIRST FLUID REAGENT, AT LEAST SOME OF SAID CONSTITUENTS PASSING THROUGH SAID SECOND BARRIER TO CONTACT A SECOND FLUID REAGENT
 9. The method according to claim 8 wherein said first reagent and said second reagent are the same.
 10. The method according to claim 8 wherein said first reagent and said second reagent are different.
 11. An apparatus adapted for chemical analysis comprising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact therewith, said apparatus having means to provide an electromotive force across said cuvette in the axial direction towards said barrier, whereby said first reagent is driven across said first barrier.
 12. An apparatus adapted for chemical analysis comprising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact therewith, said cuvette comprising the barrel of a hypodermic syringe having a needle point extending from one, the test reagent being in the far compartment relative to the needle point, the first reagent compartment being in the plunger of said syringe.
 13. The apparatus of claim 12 wherein there is provided a second reagent compartment containing a second reagent, a second porous barrier in contact with said second reagent compartment and said reagent therein, a sample chamber in said syringe adjacent said point, both said first barrier and said second barrier in contact with said sample chamber and the sample contained therein.
 14. The apparatus of claim 13 wherein said reagents are different, whereby two different tests can be run simultaneously on said sample.
 15. The apparatus of claim 12 wherein there is provided a second compartment in said plunger, said second compartment containing a reference fluid.
 16. The apparatus of claim 12 wherein said plunger is of reduced cross-section adjacent the end of said plunger nearest said point, said barrier being on the reduced cross-section of said plunger, the plane of said barrier being parallel to the axis of said plunger.
 17. An apparatus adapted for chemical analysis comprising a cuvette having therein a first porous barrier which serves to compartmentalize said cuvette, and a first test reagent fluid in a first reagent compartment in the cuvette, said barrier being in direct contact therewith, said cuvette comprising the barrel of a hypodermic syringe having a needle point extending from one end, the test reagent being in the far compartment relative to the needle point, there being a chamber in the plunger of said syringe, said chamber containiNg a reference fluid. 